Underground pipelines are a vital component of the petroleum industry, and new pipelines are continuously being constructed all around the world. In many cases, new pipleines are built in extreme climates or undeveloped regions ranging from the dense jungle to the barren desert. Because of the variety of challenges faced in the laying of pipleine and the need to ensure the continued integrity and operability of the pipeline, what would appear to be a simple operation of digging a trench and burying a pipeline is actually extremely complex.
As a pipleine is laid in a trench, care must be taken that the pipe's cathodic coating, which protects the pipe from rust and corrosion, is not damaged. Rocks and other objects normally found in the material excavated from the trench pose a threat to the integrity of this coating. Thus, it is necessary to surround the pipe with a `padding` of fine material such as sand or sifted soil to protect the pipe before the trench is filled.
One method of supplying padding material to a pipeline construction site is to transport padding material to the construction site. This often requires the hauling of heavy materials over long distances and rough terrain, adding significantly to the costs of pipeline construction and demanding excessive expenditure of time and effort. Machines have been developed to manufacture some of the padding material on-site by processing the excavated material, known as spoil, to separate oversized materials from the fine materials and returning the fine materials to the trench as padding. See, for example, U.S. Pat. No. 4,948,299 to Cronk, Jr. et al. and U.S. Pat. No. 4,912,862 to Bishop et al.
In addition, to enhance or enable the proper welding of joints between adjacent sections of pipe in a pipeline, the surface of the pipe in a region about a joint is sandblasted prior to a welding operation. This process requires substantial amounts of sand, and there are many trench sites throughout the world, for example, in rocky locales or frozen tundra regions, where it is impossible to sift enough fine material for sandblasting the pipeline joint areas. At these sites, wet sand is hauled from beaches and dried prior to sandblasting. This is a laborious and expensive process, particularly where the pipeline construction sites are far from any beaches.